This project is designed to provide information on the general characteristics of nonelectrolyte transport in the mammalian proximal tubule and in the Ehrlich ascites tumor cell. The methodology for renal studies will involve the perfusion of isolated tubule segments including the proximal convoluted tubule, and early and late segments of the proximal straight tubule. Specifically, our aims are: 1) To determine the active sites for amino acid and sugar absorption by the proximal tubule. 2) To describe the mutual dependence of Na ion and nonelectrolyte absorption. 3) To describe the potential regulatory role of nonelectrolyte absorption on salt and water absorption in the proximal nephron. 4) To determine the nature of the nonelectrolyte backflux from peritubular medium to the lumen in proximal tubules, and to describe the potential physiologic and pathologic modifiers of this backflux pathway. 5) To examine the possibility that sugars and amino acids may be actively absorbed in other nephron segments. 6) To develop mathematical models for the interrelationship between nonelectrolyte, salt and water transport. 7) To describe the mechanisms whereby cellular energy is coupled to the active accumulation of amino acids in the Ehrlich ascites tumor cell.